I am working slowly on getting ready to run challenge modes and I would like to know if some people did some research to find out which gear setup would be the most suited to do so (by suitable I mean, being able to survive critical points and still be able to do good DPS (Group healing by doing so) ?

With AskMrRobot, I runned an optimized build with Control/Mastery by removing every epic items to get a max iLvl of 463. I chose Control/Mastery because after running the simulations, the Control/Haste gave roughly 14% Haste, which might not be enough to see a difference... Here is the result:

As Gab said, any gear with sockets are great.You wont gain to much stats by having full epics compared to now cause of the scaling.But, there are chestplates, gloves, wrists, and legs with one extra socket, and waists with 2! more sockets.Not to mention raid weapons with Sha socket + the quest socket, gives you 7 extra sockets, and the str legendary socket.Thats a lot of stats.

Also, while you're at it, go to AskMrRobot's options, and enable "Enforce Hit/Expertise Caps". While the total scoring might be better being under the cap, knowing for sure that your next holy power generator is going to hit makes a lot of difference. Plus the fact that sometimes you just need to kill something in 3 hits, and if one of your 3 swings happens to be that miss, you're screwed. Most definitely worth to cap for the minuscule DPS loss you're not going to notice ever.